Scott, Vladimir and Mike,
Using only a differential model (SDD11, SDD12, SDD21, SDD22)works OK if
everything is balanced and AC-coupled. It ignores TX/RX common-mode
effects in DC-coupled architectures and system interconnects with skew
(unbalanced connector path lengths, unbalanced BGA fanouts, etc.). At
10 Gbps we can probably still get away with these assumptions but,
beyond that, I'm not sure.
Eric Sweetman
-----Original Message-----
From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Dmitriev-Zdorov,
Vladimir
Sent: Thursday, November 19, 2009 9:34 AM
To: scott@xxxxxxxxxxxxx; msteinb@xxxxxxxxxx
Cc: richard.mellitz@xxxxxxxxx; wkatz@xxxxxxxxxx; IBIS-ATM
Subject: [ibis-macro] Re: FW: [IBIS-Users] AMI convolution
Scot,
You correctly pointed out to existing limitation of the current AMI
approach. Working with single response only, we cannot consider some
effects, for example conversion of the Tx common signal into Rx
differential. The scalar waveform is thought either as voltage in single
ended connector or as differential signal in differential connection.
If we assume that all we need is difference signal at Rx input, and the
Tx's analog output assumed LTI, then we'd suffice with only two transfer
responses: diff at Tx to diff at Rx and common at Tx to diff at Rx. But
if we also decide to consider non-linearity of Tx analog output, then
we'd need a couple more, for example input admittance of the channel as
seen from Tx, both difference and common mode.
Vladimir
-----Original Message-----
From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Scott McMorrow
Sent: Thursday, November 19, 2009 10:17 AM
To: msteinb@xxxxxxxxxx
Cc: richard.mellitz@xxxxxxxxx; wkatz@xxxxxxxxxx; IBIS-ATM
Subject: [ibis-macro] Re: FW: [IBIS-Users] AMI convolution
It seems to me that a 2-port interface from a driver or receiver to the
interconnect environment would be sufficient to characterize all
multi-conductor interconnect modes, assuming that there is no
driver-to-driver, receiver-to-receiver, or receiver-to-driver analog
interactions on the silicon.
Mike Steinberger wrote:
Rich-
The output of the algorithmic model is a one dimensional waveform. If
you want to model modal behaviors, that will have to be done in the
analog model. For example, that's where the S parameter behaviors you
refer to are modeled; and depending on the EDA platform, those S
parameters can be multiconductor.
By the way, what important modes do you think should be modeled?
Mike S.
Mellitz, Richard wrote:
Hi Walter,
I was thinking about this some. Does this flow preclude a modal
impulse response flow? The single channel voltage transfer impulse
response really requires 4 entities based on s11, s21, s12, and s22.
A multi-conductor response requires more.
... Rich
*From:* ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] *On Behalf Of *Walter Katz
*Sent:* Wednesday, November 18, 2009 12:14 PM
*To:* IBIS-ATM
*Subject:* [ibis-macro] FW: [IBIS-Users] AMI convolution
All,
In case you are not in ibis-users@xxxxxxx .
Walter
Walter Katz
303.449-2308
Mobile 720.333-1107
wkatz@xxxxxxxxxx
www.sisoft.com
-----Original Message-----
*From:* Walter Katz [mailto:wkatz@xxxxxxxxxx]
*Sent:* Wednesday, November 18, 2009 12:00 PM
*To:* Eric Monteiro; ibis-users@xxxxxxx
*Subject:* RE: [IBIS-Users] AMI convolution
Eric,
Asking who is responsible for convolution is like asking who is
responsible for Fourier Transform. Convolution is a mathematical
technique that EDA tools can use on the input and output of AMI
models, and convolution is a mathematical technique that can be used
inside of the AMI model to apply a filter. The following describe who
may or must use convolution for the "Preferred Flows". Preferred
flows assume both the Tx and Rx model have Init_Returns_Filter=True
and Use_Init_Ouput=True.
Assuming a preferred statistical flow, the EDA tool supplies an
impulse response of the channel to the TX Init function. Inside the
Tx Init function (i.e. inside the AMI model), the model would compute
an impulse response of its filter and return it to the EDA tool. The
EDA tool would convolve this impulse response with the impulse
response of the channel and present these results to the Rx Init. The
Rx Init would determine the impulse response of its filter, and
return it to the EDA tool. The EDA tool would then convolve it with
the impulse response that was presented to Rx Init to determine the
impulse response of the channel equalized by both the Tx an Rx
filters. The EDA tool will process this and may use the convolution
mathematic technique (e.g. on probability distribution functions) to
generate bathtub curves and bit error rates. So in the preferred
statistical flow the EDA tool does convolution and the AMI model
might not. I could image that the AMI models may use the convolution
technique to generate the impulse response of the filter.
Assuming the preferred time domain flow, the EDA tool must first run
the statistical flow (it need not analyze the results of Rx Init).
The EDA tool supplies a stimulus waveform to Tx GetWave. The EDA tool
may or may not use the convolution generate this waveform. The Tx
GetWave will generate an equalized stimulus waveform with techniques
that may or may not use convolution. The EDA tool must us uses
convolution to apply the impulse response of the channel with this Tx
equalized stimulus waveform. The waveform is then presented to Rx
GetWave. Rx GetWave may or may not used convolution to apply its
equalization filter to it's input. The output of Rx GetWave is a
waveform, and clock ticks. The EDA tool may or may not use
convolution to analyze this waveform to generate bathtub curves and
bit error rate. So in the preferred time domain flow, the EDA tool
must use convolution, and the AMI model might not.
Walter
Walter Katz
303.449-2308
Mobile 720.333-1107
wkatz@xxxxxxxxxx
www.sisoft.com
-----Original Message-----
*From:* owner-ibis-users@xxxxxxx [mailto:owner-ibis-users@xxxxxxx]*On
Behalf Of *Eric Monteiro
*Sent:* Wednesday, November 18, 2009 10:55 AM
*To:* ibis-users@xxxxxxx
*Subject:* [IBIS-Users] AMI convolution
Hi everyone,
I was hoping someone could clarify who is responsible for convolution
in IBIS-AMI (EDA tool, or the modeler).
Clearly the convolution involving an FIR filter is upon the modeler,
the convolution I speak of is the one that is done with the channel
response.
My understanding has been as follows: (please correct me if I'm
wrong)
(a) -- (Tx IC) -- (passive channel) --(b)--(Rx IC)
You force an impulse at (a), measure the response at (b). (b) is the
analog channel response hAC(t). GetWave then needs a wave, which
should be an ideal bit train, convolved with the bit period (creates
a piece wise linear wave) which is then convolved with hAC(t) to
produce the wave fed into GetWave. There was discussion as to whether
the modeler or the EDA tool should do the above convolution. Has it
been decided who this task falls on?
Best Regards,
Eric Monteiro
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